Methyl bromide fumigation of cottonseed in freight cars for the destruction of pink bollworms

1JBKAKI

<*TATE PLANT BOARD

June 1952

E-838

United States Department of Agriculture

Agricultural Research Administration

Bureau of Entomology and Plant Quarantine

METHYL BROMIDE FUMIGATION OF COTTONSEED IN FREIGHT CARS
FOR THE DESTRUCTION OF PINK BOLLWORMS^

By G. L. Phillips,
Division of Stored Product Insect Investigations

From 1945 to 1951 experiments were carried on in Texas to determine
how methyl bromide fumigation could be utilized in the treatment of cotton-
seed originating in areas quarantined because of the pink bollworm, to
prevent it from being disseminated through transportation. Heat treat-
ment had long been the standard practice, but in many instances fumiga-
tion would be much easier.

Preliminary tests demonstrated that pink bollworm larvae embedded
in cottonseed were killed by exposure to moderate concentrations of
methyl bromide. In 1946 methyl bromide fumigation of sacked cotton-
seed intended for planting purposes was approved for use under the pink
bollworm quarantine (BEPQ 558). In a revision of this quarantine in 1948
methyl bromide fumigation of bulk cottonseed in large steel storage tanks
was approved for use. A forced circulation system was provided to
distribute the gas through the seed mass (Phillips and Bodenstein 1).
The development of a method for fumigating bulk cottonseed in freight
cars or trailer vans is described herein.

Tests on freight-car fumigation were carried on at El Paso from
1945 to 1949. During 1949 and 1950 further tests were made near San
Antonio. The first commercial evaluation tests were made at Lubbock.

All tests were made with carload lots of bulk cottonseed. In the El
Paso area no cottonseed was moved commercially by railway freight;
so it was necessary to load freight cars especially for the tests, and
then remove the seed before another loading. Cottonseed and unloading

1/ The following members of the Bureau assisted: J. K. Blocker,
A. L. Broman, J. S. Cook, Roy A. Fischer, A. H. Halverson, G. G.
Harris, P. L. Netterville, R. R. Rost, and R. S. Van Hoak. The
following members of the Texas Department of Agriculture also assisted:
C. W. Foster, G. C. Harris, and Edgar Jung. Acknowledgement is
also due to L. F. Curl, director of the Southwestern Region of the Bureau,
for his constant support of the research program.

facilities were kindly provided by the Farmers Cooperative Oil Mill at
El Paso. Tests near San Antonio were performed in carloads of seed
provided by the Swift and Company Oil Mill.

Because of the large amount of labor needed for loading and unloading
cars, locating samples, and cutting thousands of individual cotton seeds
to determine mortality (samples averaged from 13 to 60 larvae per 1,000
seeds), only a few carloads could be tested in one season.

Tests without Forced Circulation

Before the value of forced circulation was demonstrated by fumigation
in steel storage tanks, various methods were used to apply methyl bromide
in efforts to attain satisfactory distribution throughout the load of cotton-
seed. They included (1) introduction of the entire methyl bromide dosage
in the head space above the load; (2) injection of the entire dosage into the
load; (3) introduction of half above the head and injection of the other half;
and (4) application as a spray (dissolved in carbon tetrachloride) to the
surface of the load. Innovations were tried, such as partial loads, addi-
tional sealing of floors and doorways with gas-proof material, circulation
of the gas above the load, providing risers (vertical tunnels) through the
load to assist penetration of dosage applied with a blast of carbon dioxide,
and liberation of the dosage into tunnels through the load.

In most tests 1/2 -pound samples of infested cottonseed were placed
at selected locations throughout the seed mass. In some tests 30 of these
samples were used, in others 24, and in a few 15. Each sample contained
from 1,200 to 1,500 seeds and from 25 to 100 larvae. In 1948 a procedure
for drawing and analyzing gas samples was put into use. Thereafter both
seed and gas samples were taken to determine distribution.

The results are summarized in table 1. In only two tests was com-
plete mortality attained in all samples, and repeated tests with the same
procedure gave different results.

At first the data were interpreted to mean that freight cars were too
leaky to serve as good fumigation chambers. After the better methods
of sealing cars had been developed, it became evident that faulty distri-
bution of the gas was the reason for areas of low concentration.

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- 6 -

Tests with Forced Circulation

The satisfactory distribution of methyl bromide in large steel storage
tanks resulting from forced circulation prompted attempts to utilize
forced circulation in freight-car fumigation. The arrangement in the
steel tanks permitted a fairly even flow of air, or gas, through the cotton-
seed from top to bottom, because of a reduction in pressure beneath the
load as air was withdrawn from beneath the false floor, and an addition
of pressure above the load as the air was returned to the head space under
considerable velocity. Since it was not feasible to place a raised floor in
the freight car and thus permit an even reduction over the entire floor
area, air was removed from one portion of this area by means of ducts
laid on the car floor.

In the exploratory tests a blower was placed on top of the load of
cottonseed to suck air from the floor level through perforated hose
buried beneath the load. This arrangement gave fairly satisfactory
distribution, for all pink bollworm larvae were killed in the 24 samples
of cottonseed in each of the last two tests. The gas samples withdrawn
in two successful tests, in which the load was treated with 6 and 8 pounds
of methyl bromide per 1,000 cubic feet, showed the following concentrations,
in ounces per 1,000 cubic feet:

Time

6 pounds

8 pounds

30 minutes

88 -12

116 - 7

3 hours

50 - 12

68-15

6

33 - 13

56 - 19

10

33 - iu

40-16

24

17

24- 16

These tests show that, even though complete mortality was obtained
in all the samples of cottonseed, there was considerable variation in gas
ncentration at the 24 selected points. The points of low concentration
were not associated with any position in the car, although they occurred
more often at the floor level than in the body of the load. Further tests
with improved circulation were therefore undertaken.

Additional tests were made in an experimental fumigation chamber
to determine the minimum lethal concentration. The results of these
tests are given in table 2.

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-8 -

From these tests it was concluded that complete mortality of pink
bollworm larvae could be expected if the concentration could be kept
above 10 ounces per 1,000 cubic feet at all points in a carload of seed
for the first 10 hours.

A better circulation system was devised which utilized a portable
blower operated outside the car. A 4-inch duct made of downspouting and
perforated with 1/4-inch holes on three sides at 2 -inch intervals, but with
the distal end closed, was laid down the center of the car floor from end
to end before it was loaded (fig. 1). A 6 -inch side duct led from the center
to one doorway. This doorway, opposite the loading door, was sealed off
with a paper grain doori^ properly lapped and sealed gastight, and the side
duct was inserted through the paper seal (fig. 2). The ducts were then
covered by the load of seed. A portable blower (fig. 3) with a gastight
bearing was attached by 6 -inch flexible tubing to the duct protruding through
the paper seal (fig. 4). The discharge of the blower was returned to the
head space above the load by another length of flexible tubing attached to
a metal collar inserted at the top of the paper seal. A blower driven by
a 2 -horsepower motor was used. The fumigant was applied as a gas in
the discharge duct of the blower where it was carried to the head space
above the load and drawn down through the seed.

A series of six tests were made with this circulation system, with a
dosage schedule of 6 pounds per 1,000 cubic feet for 24 hours. The blower
was operated for only about 10 minutes after the fumigant was applied.
The ranges of concentration obtained are shown in table 3. Even though
the concentration at certain sampling points dropped below 10 ounces at
ine 10 -hour period, it was far above that amount after 3 hours. The fact
that these concentrations were above the minimum lethal amount was
substantiated by the fact that all larvae in the cottonseed samples were
killed.

Table 3. --Range of concentration of methyl bromide after forced-circula-
tion fumigation of freight carloads of cottonseed.

Number of

Ounces per 1,000 cubic feet after- -

samples

30 minutes

3 hours

10 hours

24 hours

21

16 - 43

14- 39

7-21

4-9

22

27- 116

15 - 112

8-33

6-14

22

20 - 114

18 - 116

7-24

6 - 11

21

37- 84

16 - 35

11-27

9-16

22

53- 93

30 - 53

14- 27

7-26

21

17- 110

16 - 69

8-21

6-13

2/ The use of the paper grain door was suggested by J. K. Blocker
and W. F. Sennette, Division of Pink Bollworm Control.

9 -

Application of Treatment for Quarantine Purposes

On the basis of these tests, fumigation of cottonseed in freight cars,
using a forced-circulation system similar to that used in the experiment,
was authorized for quarantine purposes in February 1950. As a safety
factor the dosage was set at 7 pounds per 1,000 cubic feet when the bulk-
cottonseed temperature averaged 60° F. or above. Use of the method
was limited to certain regulated areas with very light infestation where
adequate heat-treatment equipment was not available. By arrangement
any commercial use was to be supervised by the writer for the first
season, in order that improvements desirable for operation under
practical conditions might be introduced.

The Southland Cotton Oil Company used this method on approximately
12,000 tons of cottonseed to be shipped by rail from Lubbock, Tex. A
total of 306 cars were fumigated in this operation.

The same fumigation procedure was used for all cars. Only steel
freight cars in good condition were used, each one being inspected and
approved. Before being loaded, the floor of each car was covered with
sisal-kraft paper, which is gasproof, and the perforated floor duct was
put in place. The rear doorway (opposite the loading door) was sealed
with a paper grain door, and collars were inserted for the attachment
of the flexible tubing leading to and from the portable blower. Wooden
grain doors were placed in the loading door to the height of the load.
The seed was transferred from a trackside warehouse or from trucks
by a seed pump (fig. 5), in which the cottonseed is sucked up by a powerful
blower and blown through ducts into the car. The top of the load was
leveled off to give at least a 2-foot head space.

When the loading was completed, the loading door was sealed in part
with a paste made of asbestos cement and oil and in part with scotch
masking tape. The flexible blower ducts were attached to the collars
in the paper grain door. The blower, which was driven by a 5-horsepower
gasoline engine, was started, and the dosage of methyl bromide admitted
to the exhaust duct after being volatilized by passing through a coil
immersed in very hot water. The blower was operated for approximately
2 minutes after the gas was introduced and then detached. The collars
in the paper grain door were removed and the holes quickly sealed with
gasproof paper and masking tape. The car door was then closed and the
fumigation allowed to proceed for 24 hours without further attention.
The blower unit was moved to the next car to be fumigated.

As many as 16 cars were fumigated in one day, the limiting factor
being the speed of loading. One portable blower unit was considered
capable of handling 20 cars per day.

- 10 -

The actual fumigation procedure was handled by representatives of
the oil-mill company.—' The certification of the cottonseed was handled
by regular inspectors of the Bureau of Entomology and Plant Quarantined

The method developed for testing the efficiency of gas distribution in
large steel tanks, whereby two gas samples were withdrawn from a
selected sampling point at any time during the fumigation period, and the
results of analysis compared with a standard curve (Phillips and Latta 2),
was adopted as a means of observing the effectiveness of the freight-car
fumigation at Lubbock.

The lowest concentration of gas was found to be at a point near the
floor about half way between the car wall and the center duct and about
one-third the distance from the end wall to the doorway. This was
designated as the standard sampling point. A curve was plotted based
on the average of the concentrations present at this point in tests.
The lowest concentration present at this position in the experimental
cars which was associated with complete mortality in biological samples
was considered as the maximum deviation from the average.

A sample was withdrawn from a car under fumigation by inserting
a sampling probe through the paper grain door near the floor level along
a line between the center of the doorway and one of the opposite corners.
By inserting the probe 14-1/2 feet at this angle the standard sampling
point was reached consistently with accuracy. The analysis of this
sample was matched against the curve to indicate the efficiency of
distribution in each car sampled.

It was not possible to sample all cars fumigated, but an attempt was
made to sample at least half of those fumigated each day. Analyses
were made on samples from 162 of the 306 cars fumigated, and only
one fell below the maximum allowable deviation. This car was re-
fumigated.

The samples were withdrawn when convenient, so that the time of
sampling ranged from 30 minutes to 17 hours after the start of the
exposure. These concentrations at the sampling points were grouped
according to 1-hour intervals, i.e., those between 0.5 and 1.4 hours,
1.5 and 2.4 hours, etc., and an average was taken for each interval.
These data were compared with the concentrations found in the seed
mass in large steel tanks under fumigation and with the concentration
found at the standard sampling point in the experimental fumigations
as shown in figure 6.

3/ J. R. Richardson and Frank P. Dickson.

4/ Certification was supervised by H. L. Alford, M. E. Currie, and
G. W. Chowns, and performed by Inspectors T. P. Patterson, R.J.
Morits, E. L. Wilde, E. I. Fosmire, R. K. Robinson, A. S. Pela, and
Ike Laird of the Division of Pink Bollworm Control. They also assisted
the research staff in many ways as their duties permitted.

- 11 -

The fumigation of 306 carloads of cottonseed with only one rejection
and the satisfactory concentration patterns found in the sampled cars
were considered ample proof of the practicability of freight-car fumiga-
tion with the apparatus developed for forced circulation. Therefore, in
July 1950, the quarantine regulations in BEPQ 558 were further modified
to authorize freight-car fumigation in lieu of heat treatment in all lightly
infested areas in Texas, New Mexico, and Oklahoma, and as an additional
treatment for cottonseed moving from heavily infested areas.

Summary

Methyl bromide fumigation was authorized for the treatment of sacked
cottonseed in 1946, and for bulk cottonseed in large steel storage tanks
fitted with means for forced circulation in 1948. A method for fumigating
bulk cottonseed in freight cars, developed between 1945 and 1951, is
described in this paper.

Efforts were made to attain a satisfactory distribution of methyl
bromide throughout a freight-car load of cottonseed by various methods
of application, such as applying it in the head space above the load,
injecting it into the load, applying half the dosage above and injecting
half, and dissolving in carbon tetrachloride and spraying on the surface.
None were successful. Other innovations, such as partial loads, additional
sealing of floors and doorways with gas proof material, providing risers
(vertical and horizontal tunnels) through the load to assist in penetration,
and following the application with a blast of carbon dioxide, were also
unsuccessful.

Attempts were then made to adapt the method of forced circulation
used in fumigation of cottonseed in large steel storage tanks. A gas-
distribution pattern was obtained that provided a lethal concentration at
all sampling points. In the method finally adopted a portable blower
operated outside the freight car pulls air from beneath the load through
a specially designed duct system and returns it to the space above the
load. The blower is run during gas volatilization and for 2 to 10 minutes
thereafter, then disconnected, the car sealed, and the blower moved to
the next car to be fumigated.

This method for treating cottonseed was authorized for use on quar-
antined cottonseed in February 1950 in a limited area under supervision.
The dosage schedule is 7 pounds per 1,000 cubic feet for 24 hours expo-
sure at 60° F. or above, and 8 pounds at lower temperatures.

The first trial on a commercial basis was at Lubbock, Tex., where
approximately 12,000 tons of cottonseed in 306 freight cars were
fumigated. All but one of the 162 cars that were checked by gas analyses
were found to have the required gas concentration.

In July 1950 the forced-circulation method was authorized as an
alternate method for treating cottonseed for the destruction of pink boll-
worm larvae.

-12-

Literature Cited

(1) Phillips, G. L., and W. G. Bodenstein

1948. A successful large-scale experiment in methyl bromide

fumigation of bulk cottonseed for pink bollworm control.
Jour. Econ. Ent. 41: 804-805.

(2) Phillips, G. L., and Randall Latta

1949. Current use of methyl bromide for the fumigation of cotton-

seed. Down to Earth (Dow Chemical Co.) 5(1): 11-13.

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Figure 2. --Car loaded ready for fumigation,
showing collars inserted at top and bottom
of grain door.

Figure 3. --Gasoline engine mounted to drive
circulating blower. The volatilizer unit and
the scales for weighing dosage are also
shown.

- 15

Figure 4. --Volatilizer and circulating unit
attached to one of several loaded cars ready
for fumigation. The unit could handle one
car in 15 to 18 minutes.

Figure 5. --Portable seed blower transferring
cottonseed from a truck to a freight car.

- 16

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Figure 6. --Methyl bromide concentrations at standard sampling points in com-
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